The present invention relates generally to a process for rapidly predicting a metallographic structure, such as the degree of nodularity, of castings to be made from molten metal before casting and apparatus for performing the same.
It is known that the composition of molten metal may be estimated by recording the liquidus and eutectic temperatures using known cooling curves. Such method provides information such as a change in phase, carbon equivalent, etc. It is also known to determine the thermal conductivity of solid bodies by measuring the heat flow through such body when subjected to a thermal gradient.
It has been observed that in grey cast iron in the solid state, the thermal conductivity is substantially influenced by the graphitic structure and that a nodular cast iron, for instance, has a lower conductivity than a lamellar or equivalent composition.
When pouring cast iron, it is important that analysis be carried out very quickly and before casting. If one waits too long before completing a pour of a nodular cast iron, a large percentage of the magnesium which is present in the molten metal will dissipate or will otherwise be lost and there is a likelihood of making an unsatisfactory cast.
The industry has long sought a simple, rapid and effective way of accurately predicting the degree of nodularity of a cast iron before casting of the same. One method proposed heretofore is disclosed in U.S. Pat. No. 3,670,558 wherein the properties of a nodular cast iron are evaluated by way of a comparative study of conventional cooling curves and a set or family of curve segments. The method proposed by said patent has not proven to be acceptable.
Thus, at the present time, the degree of nodularity of a cast iron can only be determined with precision if the sample is cooled and evaluated by ultrasonic or metallographic analysis, and the like.
The main object of the present invention is to cope with said problem by proposing a new process and apparatus making it possible to predict in a simple, rapid and effective manner the degree of nodularity of the cast iron casting while the iron is still molten and while it is still possible to change the composition of the molten metal or it is possible to scrap the molten metal.